I need to find the "d" value in arithmetic sequence

I have: -7, -2, 3, 8

I know D= difference.
And you need to do like: I want to find this term so that'd be my x (unknown)
and then i would have these numbers what i know are right?
Or something like that??

nth term in an arithmetic progression is a + (n-1)d
a = -7
d = 5
so select the term you want to find and sub that number in the equation.

Well if the answer you need to know is the difference between each of the numbers in the sequence, that's easy. It's 5. The difference between -7 and -2 is obviously 5. If that isn't the answer you're looking for I'm at a loss.